Hot dip plating method and apparatus



8- 1954 J. E. BUTLER I 2,686,135

HOT DIP PLATING METHOD AND APPARATUS Filed Jan. 24, 1949 2 Sheets-Sheetl Fig.2.

N a7 INVENTOR. JOHN E. BUTLER 33 5:

g- 1954 J. E. BUTLER 2,686,135

HOT DIP PLATING METHOD AND APPARATUS Filed Jan. '24, 1949 2 Sheets-Sheet2 INVENTOR.

JOHN E. BUTLER Patented Aug. 10, 1954 HOT DIP PLATING APPARA Weirton, W.Va., assignor to N John E. Butler,

METHOD AND TUS tional Steel Corporation, a corporation of DelawareApplication January 24, 1949, Serial No. 72,471

This invention relates to an improved methof and apparatus for hot dipplating sheets of base metal with a coating of protective metal and moreparticularly relates to the removal of excess'molten metal from thetrailing edges of the plated sheets.

The present invention will be described in connection with the hot dipplating of sheets of base metal, such as sheets of blackplate, with aprotective coating of tin. In the production of tin plate by the hot dipprocess, the sheets of blackplate are passed through a bath of moltentin and then up through a body of hot grease, such as palm oil, floatingon the surface of the molten tin. Finishing rolls are mounted in thelayer of palm oil for regulating the thickness of the tin coating. Thehot palm oil serves as a medium in which to keep the tin coating moltenon the sheet so as to produce better tin distribution. The

palm oil also aids protecting the tin from oxidation. The oil or greaseis at an elevated temperature, and the tin coating is not solidified inthe palm oil. It is to be understood that the present invention is notlimited to blackplate for the sheets of base metal or to tin as theprotective coating metal or to palm oil or grease as the protectiveliquid. Other metals which have a melt-- ing temperature below thatofthe base metal may be used, and other hot liquids may be used in placeof the palm oil depending on the type of metal and other factors. Theprotective liquid should not dissolve the coating metal.

In the hot dip process of plating or coating sheets with a layer ofprotective tin, the sheets are passed through a bath of molten tin. Thecoated sheets are Withdrawn from the bath and have thereon a uniformcoating of tin except for the trailing edge which is last to leave thebath. The trailing edge portion has a relatively thicker coating and iscommonly known as the list edge. The formation of this list edge is awaste of relatively expensive coating metal and results in sheets thatare non-uniform. While various procedures have been proposed forpreventing the formation of this list edge, these prior art procedureshave had various drawbacks, and, insofar as is known, none has been usedcommercially; and all commercially produced hot dip plate, such as tinplate, galvanized sheets, terne plate, and sheets coated with aluminumhave this relatively thicker list edge.

Accordingly, it is an object of the present invention to, provide anovel method of and apparatus for producing hot dip coated sheets havingon the edge portions a coating which has the Claims. (Cl. 117-102) sameor more nearly the same thickness as the coating on the remaining, majorportions of the sheets. 1

Another object of the present invention is to provide a method of andapparatus for removing the excess metal from the sheetswlhout damagingor marring the sheets.

Another object of the present invention is to provide a method of andapparatus for removing excess metal from the trailing edge portion ofhot dip plated sheets While the trailing edge portion is submerged inthe layer of hot protective liquid, palm oil, floating on the bath ofmolten metal and before the coating metal solidifies and then utilizingthe removed molten metal in the metal bath.

Another object of the present invention is to remove the excess moltenmetal from the list edge without exposing the molten metal to theatmosphere and thereby reducing oxidation of the molten metal and toeiiect such removal while the molten metal is relatively nuid before themetal is solidified or unduly thickened so that the molten metal willreadily W and smooth out any surface irregularities.

In accordance with the present invention, a sheet of base metal such asblackplate is passed through a bath oi molten tin and then up through alayer of hot palm O11 floating on the surface of the tin bath. The sheetcoated with molten tin is Withdrawn from the hot palm oil, and themolten tin then quickly solidifies. Before the trailing edge leaves thepalm oil and While the tin is in a hold condition, the excess moltenmetal is removed. Removing the excess tin in the palm oil has a numberof advantages. The tin coating While in the hot palm oil is more fluidthan after the sheet is Withdrawn, and any imperfections or surfaceirregularities quickly disappear as a result of the ability of the fluidtin to smooth itself out into a film having a level surface. As soon asthe coated sheet is withdrawn from the palm oil, the tin thickens andquickly solidifies, and any disturbance in the surface of the tin atthat time tends to remain permanently. The removed molten metal sinksunder the influence of gravity down through the palm oil and returnsdirectly to the bath of molten tin. The removed molten tin is notexposed to the atmosphere and oxidized, and there is no handling loss.By forming a coating on the trailing edge that is the same or morenearly the same thickness as on the remainder of the sheet, the amountof tin required per sheet is reduced,

and the coated sheet has a more uniform thickness.

These and other objects and advantages will become more readily apparentfrom the follow ing detailed description, taken with the accompanyingdrawings, in which:

Figure l is a vertical sectional view of hot dip, tin plating apparatusembodying the principles of the present invention;

Figure 2 is a horizontal sectional view taken along line 22 of Fig. 1;

Figure 3 is a fragmentary sectional view similar to Figure 1illustrating another embodiment of the present invention;

Figure 4 is a fragmentary sectional view taken along line 4-4 of Figure3;

Figure 5 is a fragmentary sectional view similar to Figure 1illustrating another embodiment of the present invention; and

Figure 6 is a fragmentary sectional view taken along line 6-6 of Figure5.

Referring more particularly to Figures 1 and 2 of the drawings and theembodiment of the present invention shown therein, thi hot dip tinplating apparatus includes a tank H3 through which a series of similarsheets Ii are successively passed and coated with molten tin. Sheets iiare fiat sheets of ferrous metal containing a low percentage of carboncommonly termed black plate.

The tank l includes a relatively lower tin pot 12 in which there ismaintained a pool or bath of molten tin 13'. A pair of upper plates isextend across the tank and form a flux pot which confines a pool of fluxl on the surface of the bath 33 of molten tin. The sidewalls of arelatively higher grease pot it are arranged to confine a layer ofgrease, such as palm oil, on the bath of molten tin $3 in the tin pct52. Two pairs ,of power-actuated feed rolls is are provided for feedingthe sheets H one by one down through the body of flux i5 and into thebath 53 of. molten tin. A pair of power-actuated feed rolls or tin potrolls 2!) are mounted in the tin pot l2 along with guides 2i and 22 allarranged to move the sheets H through the molten tin and then up intothe grease pot. Three pairs of power-actuated rolls 2,3, 2 and 25 aremounted in the grease pot l6 and in the layer of palm oil. Theselast-mentioned pairs of rolls move the sheets from the tin pot upthrough the grease pot. The pairs of rolls 23, 2d and 25 are alsofinishing rolls, and the pressure of the rolls on the coated sheetsdetermines, at least to a certain extent, the thickness of the tincoating on the finished sheets by removing or wiping of the excessmolten metal. These finishing rolls do not prevent the formation of therelative thicker list edge.

The tin plating apparatus includes a pair of upwardly extending sideplates 21 mounted on the tank [9. Power-actuated catcher rolls 2?! arerotatably mounted in plates 2? in position to receive the upper leadingedge of each sheet as it is fed upwardly out of the grease pct 56 by thefinishing rolls. The tin coating usually is sufficiently solidified bythe time the sheets reach the catcher rolls so that the catcher rolls itdo not mar the surface of the sheet. A roll 39 is provided for guidingthe sheets ll from the catcher rolls 29 to a guide chute 3! from whichthe sheets pass to other units in the processing line or to sorting andinspection stations.

The apparatus shown and described in the drawings is of the typeintended to simultaneously pass two series of sheets ll through the tinpot and grease pot to the catcher rolls. As described so far, theapparatu is of conventional type and will be described as though onlyone series of sheets were plated, it being understood that the secondseries of sheets are simultaneously plated in the same manner. Insofaras the present invention is concerned, it is immaterial whether one ormore than one series of sheets are simultaneously plated.

The sheets H passing up through the grease pot have thereon a coating ofmolten tin, The hot protective liquid, palm oil, maintains the tinmolten but cools the molten tin without solidifying the tin so that asthe sheet leaves the grease pot the molten tin will quickly solidify andwill not be as readily oxidized by the atmosphere. At times, it iconventional practice to direct streams of cooling air against thesheets passing from the grease pot rolls to the catcher rolls as an aidin cooling the tin.

Sheets of tin plate produced as described have relative thicker listedges on which there is a heavier coating of tin. In the grease pot I6,there is mounted a rod 63 connected at each end to a vibrator means 3%.The vibrators 34 may be of the customary type available on the marketfor vibrating members or may be of special design. The vibrators 34vibrate the rod 33 quite rapidly. Below the rod 33 and above the rolls25, there is mounted an electromagnet 35. The rod 33 and magnet 35 arepositioned closely adjacent to the path of the sheets passing from therolls 25 to the catcher rolls 29. The rod 33 and magnet 35 are spacedslightly from this path so that unless the sheet ll moves from this paththe sheet will not touch rod 33, The magnet 35 is connected to a sourceof electric current and sets up a magnetic field tending to attract thepassing sheet toward the rod 83. Although the sheet H is flexible andthe magnet is positioned close to the rolls 25, the magnet does notexert sufficient magnetic force to move the leading edge portionlaterally from the normal path of sheet movement against the rod 33. The.rolls 25 preferably support the leading edge portion sufliciently toprevent contact between sheet H and the rod 33. As the sheet movesupwardly, the leading edge passes between the catcher rolls. When thetrailing edge leaves the finishing rolls, the sheet is supported by anddepends from the catcher rolls 29. A relatively long portion of thesheet is not supported against lateral movement, and the magnet 35 drawsthe trailing edge of the sheet against the vibrating rod 33substantially as shown in the drawings, The rapidly vibrating rod 33 inturnvibrates the trailing edge of the sheet and removes the excessmolten tin. The removed tin sinks through the hot palm oil and returnsto the tin pot l2. The sheets II are moved quite rapidly by the poweractuated rolls so that the period of contact between the trailing edgeportion and the vibrating rod 33 is brief but sufiicient to removeexcess molten metal.

The coating of tin on the trailing edge of the sheet at the time ofcontact with rod 33 is more fluid than after the sheet leaves the layerof palm oil l'i. If there is any surface disturbance on the coating inthe palm oil, the coating is sufiiciently fluid to fiow and smoothitself. In addition, the removed tin is not oxidized by exposure to theatmospheric air and returns directly to the tin pot so that there iscomplete recovery of the removed tin. The finished sheet has arelatively more uniform thickness and a given amount of tin will coat agreater surface area.

Referring more particularly to Figures 3 and 4 of the drawings, theapparatus, shown in part, is similar to that of Figures 1 and 2 andidentical parts have applied thereto the same reference numerals. Theembodiment of Figures 3 and 4 does not include a magnet 35'as does theapparatus of Figures 1 and 2 but does include a vibrating rod 33 whichis vibrated by vibrators 34 that may be of any suitable type. Above thetin pot I6, there is a pair of catcher rolls 31 positioned to receivethe sheet II passing upwardly from the upper finishing rolls 25 and aguide roll 38 for guiding the sheet to guide chute 3|. The catcher rolls3! are arranged with their axes parallel to the axes of rolls 25 and thenip of rolls 3'! is in alignment with the pass line of rolls 25. Theroll 31 which is on the opposite side of the path of the sheets from rod33 has its axis below that of the other roll 31. Thus, the pass line ofthe rolls 3? is at an angle to the path of the sheets so as to urge ortend to urge the portion of sheet II that is below the catcher rollstoward the vibrating rod 33. As the finishing rolls 25 move a sheet llupwardly, the leading edge enters the nip of rolls of 31 and then passesbetween the catcher rolls. As soon as the trailing edge leaves rolls 25,it moves toward the left and against rod 33. The rod 33 vibrates thetrailiing edge and removes the excess molten metal which passes downthrough the layer I! of palm oil to the tin pot as described inconnection with Figures 1 and 2.

The apparatus of Figures 5 and 6 is'the same as the apparatus of Figures1 and 2 except for the means for vibrating the trailing edge portions ofthe sheets ii and the same reference numerals have been applied to theidentical parts. In the apparatus of Figures 5 and 6, the means forvibrating the trailing edge of each sheet includes a plurality ofvibrators it submerged in the body of palm oil i'i. Each vibrator 40 hasa plunger 4!, the outer end of which is positioned closely adjacent tothe path of the sheets between the finishing rolls and catcher rolls.The vibrators 43 are positioned on opposite sides of the sheet path, andthe plungers 4! do not touch the sheet but vibrate the sheet,particularly the trailing edge, as a result of transmission of thevibrations of plungers ii through an intervening layer of palm oil sothat there is no direct contact between the vibrators and the sheet. Thevibrators 40 may be suspended in the palm oil by any suitable means andare preferably operated by electrical power. The rate of vibration ofthe plungers 4! may be within the audible range or may be ultrasonic,depending in part on the space between the plungers and sheet and thearea of the ends of the plungers and the thickness of the sheet.

In each of the embodiments shown and described, the trailing edge of thesheet is vibrated in the palm oil while the sheet is suspended by anddepending from the catcher rolls so that the trailing edge is free tovibrate. While this construction is preferable, it is to be understoodthat the vibrating means, and particularly the vibrators of Figures 5and 6, may be positioned below-the lowest finishing rolls or between thegrease pot rolls. For example, if desirable, the grease pot rolls couldbe spaced farther apart and the vibrating means placed between the rollswith the upper pair or pairs of grease pot rolls acting substantiallythe same as the catcher rolls.

In each embodiment of the present invention,

the trailing edge of the sheet is vibrated While in the palm oil toremove excess molten tin. The removed molten tin is not exposed to theair and is returned to the tin pot without being oxidized in whole orpart. Further, when the excess tin is removed, the tin coating isrelatively more fluid and the tin more readily flows to smooth out anyvariations in coating thickness.

In the drawings, the thickness of the sheets has been exaggerated tomake a better showing. In addition, the sheets will engage the guide 22and be bent and guided upwardly thereby, although for purposes ofgreater clarity, the sheets are shown as slightly spaced from thisguide. The drive mechanism for the rolls has been omitted as thismechanism is of conventional construction of the same general design asused commercially on hot dip tin plating apparatus of the type shown anddescribed.

I claim:

1. In the hot dip process of coating a metal sheet with a layer ofmetal, the steps comprising, passing such a sheet through a bath ofmolten metal to coat the sheet and then passing the coated sheetupwardly through a layer of liquid on the bath, the coating metal on thesheet in the layer of liquid being molten and the liquid being anonsolvent for the molten metal, and rapidly vibrating the trailing edgeof the sheet in the liquid layer to remove excess molten coating metalwhile the sheet is suspended with its trailing edge free to vibrate inthe layer of liquid.

2. In the hot dip process of coating a ferrous metal sheet with a layerof tin, the steps comprising, passing such a sheet through a bath ofmolten tin to coat the sheet and then passing the coated sheet upwardlythrough a layer of hot palm oil on the bath, the coating of tin on thesheet in the layer of palm oil being molten, and rapidly vibrating thetrailing edge of the sheet in the layer of palm oil to remove excessmolten tin from the trailing edge portion of the sheet.

3. In the hot dip process of coating a metal sheet with a layer ofmetal, the steps comprising, passing such a sheet through a bath ofmolten metal to coat the sheet and then passing the coated sheetupwardly through a layer of liquid on the bath along a predeterminedpath, the coating metal on the sheet in the layer of liquid being moltenand the liquid being a nonsolvent for the molten metal, applyingmagnetic force against the trailing edge of the sheet as the trailingedge moves through the liquid layer and displacing the trailing edgelaterally from said path, and rapidly vibrating the displaced trailingedge of sheet in the liquid layer to remove excess molten coating metal.

4. In the hot dip process of coating a metal sheet with a layer ofmetal, the steps comprising, passing such a sheet through a bath ofmolten metal to coat the sheet and then passing the coated sheetupwardly through a layer of liquid on the bath along a predeterminedpath, the coating metal on the sheet in the layer of liquid being moltenand the liquid being a nonsolvent for the molten metal, changing thedirection of travel of the leading edge sheet and displacing thetrailing edge of the sheet laterally from the predetermined path whilethe trailing edge is in the layer of liquid, and rapidly vibrating thetrailing edge of the sheet in the liquid layer to remove excess moltencoating metal.

5. In the hot dip process of coating a metal sheet with a layer ofmetal, the steps comprising,.passing such a sheet through abath' ofmolten metal to coat the sheet and then passing the coated sheetupwardly through a layer of liquid on the bath, the coating metal on thesheet in the layer of liquid being molten and the liquid being anonsolvent for the molten metal, and rapidly vibrating the trailing edgeof the sheet in the liquid layer to remove excess molten coating bysetting up a source of vibrations in the liquid layer and impartingvibrations to the trailing edge through an intervening layer of liquid.

6. In the hot dip process of coating a sheet of base metal with a layerof protective metal, the steps comprising, passing such a sheet througha bath of molten protective metal to coat the sheet and then passing thecoated sheet upwardly through a layer of liquid on the bath and be-,tween and in engagement with pairs of finishing rolls located in thelayer of liquid, the coating metal on the sheet in the layer of liquidbeing molten and the liquid being a non-solvent for the moltenprotective metal, and rapidly vibrating the trailing edge of the sheetwhile in the liquid layer above the finishing rolls to remove excessmolten metal from the trailing edge while the sheet is suspended withits trailing edge free to vibrate in the layer of liquid.

7. In apparatus for coating a metal sheet with a layer of protectivemetal, the combination comprising, tanlr. means including relativelylower pot means arranged to confine a bath of molten protective metaland relatively higher walls ar ranged to confine a layer of protectiveliquid on top of the bath of molten metal, means for moving the sheetthrough the bath of molten metal and then upwardly through the layer ofliquid along a predetermined path, sheet vibrating means adjacent butspaced from said path below the top of the liquid-confining walls, andmagnetic means positioned adjacent the path for urging the trailing edgeof the sheet against the sheet vibrating means upon energization torapidly vibrate the trailing edge portion of the sheet in the layer ofliquid and remove excess molten coating metal.

8. In apparatus for coating a metal sheet with a layer of protectivemetal, the combination comprising, means for moving the sheet throughthe bath of molten metal and then upwardly through the layer of liquidalong a predetermined path, sheet vibrating means adjacent but spacedfrom said path below the top of the liquidconfining walls, and a pair ofrolls disposed above the tank means in position to receive the upwardlymoving sheet, said rolls being rotatable about parallel axes and thepass line of said rolls being angularly disposed to said path so thatthe rolls urge the trailing edge of the sheet against the vibratingmeans to rapidly vibrate the trailing edge portion of the sheet in theliquid layer and remove the excess molten coating metal.

9. In apparatus for coating a metal sheet with a layer or" protectivemetal, the combination comprising, means for moving the sheet throughthe bath of molten metal and then upwardly through the layer of liquidalong a predetermined path, and sheet vibrating means arranged onopposite sides of and spaced from said path below the top of theliquid-confining walls and the surface of the liquid layer, saidvibrating means being arranged to rapidly vibrate the trailing edgeportion of the sheet in the layer of liquid through an intervening layerof liquid and remove excessmolten coating metal wlthouttouching thesheet.

10. In apparatus for coating a metal sheet with a layer of protectivemetal, the combination comprising, means for moving the sheet throughthe bath of molten metal and then upwardly through the layer of liquidalong a predetermined path, a member adjacent but spaced from said pathextending transversely of the path of the sheet and below the top of theliquid-confining walls and the upper surface of the layer of liquid,means for rapidly vibrating the member. and means positioned adjacentthe top for urging the trailing edge of the sheet against the member tovibrate the trailing edge in the layer of liquid and remove excessmolten metal.

11. In apparatus for coating a metal sheet with a layer of protectivemetal, the combination comprising, means for moving the sheet throughthe bath of molten metal and then upwardly through the layer of liquidalong a predetermined path, a member adjacent but spaced from said pathextending transversely of the path of the sheet and below the top of theliquid-confining walls and the upper surface of the layer or liquid,vibratory means for vibrating the member, and magnetic means positionedadjacent the path for urging the trailing edge of the sheet against thevibratory means upon energizaticn to rapidly vibrate the trailing edgeportion of the sheet in the layer of liquid and remove excess moltencoating metal.

12. In apparatus for coating a metal sheet with a layer of protectivemetal, the combination comprising, means for moving the sheet throughthe bath oi molten metal and then upwardly through the layer of liquidalong a predetermined path, a member adjacent but spaced from said pathextending transversely of the path of the sheet and below the top of theliquid-confining walls and the upper surface of the layer of liquid,means for vibrating the member, and a pair of rolls disposed above thetank means in position to receive the upwardly moving sheet, said rollsbeing rotatable about parallel axes and the pass line of said rollsbeing angularly disposed to said path so that the rolls urge thetrailing edge of the sheet against the vibrating means to rapidlyvibrate the trailing edgeportion of the sheet in the liquid layer andremove the excess molten coating metal.

13. In apparatus for coating a ferrous metal sheet with a layer of tin,the'combination comprising, tank means including relatively lower tinpot means arranged to confine a bath of moltentin and relatively highergrease pot means arranged to confine a layer of palm oil on top of thebath of molten tin, means for moving the sheet through the bath ofmolten tin and then upwardly through the layer of palm oil along apredetermined path; said sheet moving means includingpower-actuatedrolls positioned inside of the grease pot means below thesurface of the palm-oil, roll means spaced above the tank means inposition to receive the upwardly moving sheet and support the sheet withits trailing edge portion free of the power-actuated rolls, a memberadjacent but spaced from said path extending transversely of the path ofthe sheet and below the top of the grease pot means and the uppersurfaceof the layer of palm oil, means for vibrating'said'member, andmagnetic means positioned adjacent the path for urging the trailing edgeof the coated sheet against the member upon energization to rapidlyvibrate the trailing edge portion of the" sheet in the layer of palmoil-andremove excess molten tin.

141 111 apparatus for coatingaferrous' metal sheet with a layer of tin,the combination comprising, tank means including relatively lower tinpot means arranged to confine a bath of molten tin and relatively highergrease pot means arranged to confine a layer of palm oil on top of thebath of molten tin, means for moving the sheet through the bath ofmolten tin and then upwardly through the layer of palm oil along apredetermined path, said sheet moving means including power-actuatedrolls positioned inside of the grease pot means below the surface of thepalm oil, a member adjacent but spaced from said path extendingtransversely of the path of the sheet and below the top of the greasepot means and the upper surface of the layer of palm oil, means forvibrating the member, and a pair of rolls disposed above the tank meansin position to receive the upwardly moving sheet, said rolls beingrotatable about parallel axes and the pass line of said rolls beingangularly disposed to said path such that the rolls urge the trailingedge of the sheet against the vibrating member to rapidly vibrate thetrailing edge portion of the sheet in the layer of palm oil and removethe excess molten tin.

15. In apparatus for coating a ferrous metal sheet with a layer of tin,the combination comprising, tank means including relatively lower tinpot means arranged to confine a bath of molten tin and relatively highergrease pot means arranged to confine a layer of palm oil on top of thebath of molten tin, means for moving the sheet through the bath ofmolten tin and then upwardly through the layer of palm oil along apredetermined path, said sheet moving means including power-actuatedrolls positioned inside of the grease pot means below the surface of thepalm oil, roll means spaced above the tank means in position to receivethe upwardly moving sheet and support the sheet with its trailing edgeportion free of the power-actuated rolls, and sheet vibrating meansarranged on opposite sides of and spaced from said path below the top ofthe grease pot and below the surface of the layer of palm oil, saidvibrating means being arranged to rapidly vibrate the trailing edgeportion of the sheet in the layer of palm oil through an interveninglayer of palm oil and remove excess molten tin without touching thesheet.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 811,854 Lee Feb. 6, 1906 854,006 Steele May 21, 1907 2,026,598Taylor Jan. 7, 1936 2,080,494 Martindell May 18, 1937 2,326,372 LignianAug. 10, 1943

1. IN THE HOT PRESSURE OF COATING A METAL SHEET WITH A LAYER OF METAL,THE STEPS COMPRISING, PASSING SUCH A SHEET THROUGH A BATH OF MOLTENMETAL TO COAT THE SHEET AND THEN PASSING THE COATED SHEET UPWARDLYTHROUGH A LAYER OF LIQUID ON THE BATH, THE COATING METAL ON THE SHEET INTHE LAYER OF LIQUID BEING MOLTEN AND THE LIQUID BEING A NONSOLVENT FORTHE MOLTEN METAL, AND RAPIDLY VIBRATING THE TRAILING EDGE OF THE SHEETIN THE LIQUID LAYER TO REMOVE EXCESS MOLTEN COATING METAL WHILE THESHEET IS SUSPENDED WITH ITS TRAILING EDGE FREE TO VIBRATE IN THE LAYEROF LIQUID.